With John McCain's poll numbers tanking as fast as the Dow, it's no surprise that his campaign has decided to dust off some of the inflammatory character attacks that Hillary Clinton's campaign debuted back during the primaries. The latest is this: designated attack dog Sarah Palin's reworked stump speech now accuses Obama of "palling around with terrorists who would target their own country."

One might note at the outset that Obama has had dealings with just one domestic terrorist—former Weather Underground member Bill Ayers—and that "palling around" is hardly a good description of this passing acquaintanceship. Obama and Ayers were both politically active members of Chicago's Hyde Park neighborhood, and both were affiliated with the neighborhood's University of Chicago. But the very New York Times article that Palin cited as a source concluded that "the two men do not appear to have been close."

So Palin’s "palling around" accusation is no more true than her boast that she "told congress ‘Thanks, but no thanks’" on the Bridge to Nowhere, or that she had the Alaska Permanent Fund divest from Sudan. But it seems to me that pointing out factual errors gives this line of argument too much credit: guilt by association, even when the association happens to be real, is a silly charge.

In 1995 Obama and Ayers really were both involved with the Chicago Annenberg Challenge—part of a national school reform effort financed by the publisher Walter Annenberg—along with various others, including the state's Republican governor. As it happens, Ayers’s and Obama’s relationship in this endeavor was no more than incidental. But suppose it had been more than that? Suppose Obama, a state legislator interested in urban problems, and Ayers, an education professor, had collaborated intensively on some local education project. What difference would it make?

The very same Times article observes that Chicago Mayor Richard Daley has "long consulted Mr. Ayers on school issues" and quotes him as saying that Ayers has "done a lot of good in this city and nationally." Whether that's a good thing or a bad thing should, surely, be determined by the quality of Ayers' advice about education policy rather than his views on whether or not a domestic bombing campaign was a morally acceptable response to the United States' wrongheaded prosecution of the Vietnam War. (For the record: it wasn't.)

If there were reason to believe that Obama harbored intentions of appointing Ayers to a national security post, or of using the powers of the presidency to orchestrate a bombing of the Pentagon, then there would be important questions to raise during a political campaign. But the idea that merely knowing somebody who has radical opinions ought to constitute a devastating objection to someone's political career is both wrongheaded and dangerous.